Plasma sources are well known. An example is described in WO2008055993 assigned to Dublin City University. In this arrangement a plasma reactive impedance element that is formed from a plurality of unique tiles is described. The tiles are arranged such that immediately neighbouring tiles are coupled out of phase with one another. In this way wavelength effects that are traditionally associated with plasma sources may be minimised.
Within the context of such plasma sources there are however issues encountered regarding specifics of the tile design. For example between immediately neighbouring tiles capacitive coupling may impact deposition profiles under the tiles in that pattern effects may be transferred from the tiles onto the film which is being treated within the plasma chamber. Within the area proximate to tile boundaries there is a possibility of plasma formation which can result in increased deposition in these areas as opposed to the regions immediately below the tile centres—this can obviously affect the consistency of deposition. Furthermore edge coupling effects between tiles are dependent on plasma conditions. While this can be addressed by minimizing the actual dimensions of the individual tiles there is the corresponding result for large plasma areas of requiring too many tiles.
For these and other reasons there is a requirement for an improved electrode for use in plasma sources.